Winter Model Discussion Thread 12Z onwards 5/1/13

[Met4Cast]

The ensembles are often too slow to pick up the signal which make the Operationals look like outliers. I remember back in 2009 the ensemble suite was fairly mild whilst the operationals were gunning for cold - Every single ensemble member jumped from mild to cold in a single run.

Obviously I'm not saying that's going to happen here, but it's worth keeping in mind - At the moment though, I'd say turning cooler through next week, perhaps cold by the weekend.

[SnowObsessor90]

It does make you feel that we might be being lead up the garden path ever so slightly, I hope this doesn't turn into a 2-3 day cold snap like we had back in early Dec and we end up back to milder conditions soon afterward

Well according to some of the more knowledgeable on here this upcoming shot at cold may not be literally win or bust unlike early with December with further opportunities being possible not too long afterwards. Are those background signals right though?, I guess we'll just have to wait and see.

Edited January 6, 2013 by Anonymous21

[ITSY]

slightly disappointing ens IMO, with not many going for substantial Ely or, perhaps more important, a Greenland block further down the line ala ECM. Not a bad day at the office though for this thread, certainly some more immediate possibilities to get stuck into in the coming week. Night all.

[pyrotech]

So the Operational runs tonight all seem to favor cold, including the control runs...but the Ensembles for both the ECM and the GFS are telling us that these solutions are the coldest and likely the best case scenario's.

It does make you feel that we might be being lead up the garden path ever so slightly, I hope this doesn't turn into a 2-3 day cold snap like we had back in early Dec and we end up back to milder conditions soon afterward

Time will tell, but I for one am enjoying the eye candy, but treating it as nothing more than that at this stage

I agree that they are the coldest runs and maybe outliers

However they are the runs based on actual changes and reading, without modification.

So maybe in this unusual senario they are closer to the mark, i say this because we look at the other members, which assume different readings due to inaccuracy over an area. So just may be the changes happening in the atmosphere are showing and due to PV are fairly acute, but modification would make them more or less acute. This is where i would expect the operational to be closer to the mark even as an outlier, thats if the changes are happening already in a way that the data can be collected for the computers. With such wide variations happening i would expect the computers to under estimate as its against the norm, We could see the outlier operational also under estimated, if it is then again the final outcome would be very different, and not nessisarily in a good way.

For the models an inch wrong today is a mile by tomorrow.

But the pub run by gfs along with ECM 12z is very good, but better if they got there same way.

[pyrotech]

Well according to some of the more knowledgeable on here this upcoming shot at cold may not be literally win or bust unlike early with December with further opportunities being possible not too long afterwards. Are those background signals right though?, I guess we'll just have to wait and see.

The signals are there, without doubt.

Problem is how the vortex splits and where blocking forms and builds. Some places in NH will see a very cold period, i will put my name on that, problem can be if the building blocks are in wrong place we can easily lose out.

I will try to explain it

We have a truck traveling along M4 we are going to ask it to stop

The truck is the PV, like the truck we know it will stop or split in case of Pv.

We know somewhere on NH blocking will form due to disrupted PV, same with truck it will stop between where it is now and somewhere between its current position and mile ahead.

With the truck we now have unknowns

1. thinking distance ( time to apply brakes) time SSW takes to disrupt vortex

2 tyre tread ( grip to stop truck) orientation of vortex when split

3. weight of truck - The amount of warming propogated to surface

4, drivers urge to stop ( pressure on brakes) Is it a constant wave, or multiwave

So with the truck we know it will stop, we can estimate between point A and B , where we know it will not be emediate so we move our starting point slightly away from A

As we see the truck begin to stop we can get a better idea, however we still can not predict fully, because the driver has ability to change all the constants by easing on or off the brakes.

That can be a second or third wave, so as you can see until that truck begins to stop its dificult to predict stopping distance, even then other drivers can influence changes along the way.

Thats why models are struggling, but two models showing cold may mean that they have some constants ruled in now and getting suggestions on where this will end up, but i see both models using differnt formulas for this truck right now, however they both get it to within a few metres.

If it stops in wrong place blocking could cause a zonal cold spell or blocked Zonal for us with Low pressure stuck to our west driving mild air and rain, if it stops in right place we get the cold we dream of.

[Robbie Garrett]

I fly as a qualified pilot, you've always got to forecast likely......

But anyways, It's likely. Such as well might happen or be true; probable. I am not misleading people. If we go on about saying nothing past 120 hours will be correct, when It could be correct to some extent we might as well forget about it. =)

With the greatest respect, please don't mislead people by saying that snow events are "likely" for the southeast on the 14th. Uncertainty is high at +120 hours, let alone about +250 hours!

Think he means based on that chart alone

[Dave Kightley]

If the GFS 18z or ECM 12z are right then this cold spell could be Huge! Going round my head is it could start on the 11th with further warming forecast for 17th with another maybe end of the month. Shouts plenty of snow chances! mild blips il accept if the uppers are colder afterwards.

Edited January 6, 2013 by Dave Kightley

[Panayiotis]

Heights to the north have strengthened quite a lot since the 18z which again is always good also notice that little low to the south which wasnt there on the 18z, I dont know however what role if any it will play, maybe another good run to follow?

Edited January 6, 2013 by Panayiotis

[Panayiotis]

So the little low to the south that I was on about in my previous post seems to be taking the undercut route. Interesting if does do this!

Edit: At 123hrs it does and also heights are being sent northwards towards the Greenland area earlier on this run!

Edited January 6, 2013 by Panayiotis

[swfc]

Ridging in atlantic looks much stronger at 138 hrs.atlantic should be locked out shortly

[Panayiotis]

Normally we see our signal for colder weather becoming downgraded as we head to the day, this seems to be the opposite, lots of upgrades in this run already!

Edited January 6, 2013 by Panayiotis

[Met4Cast]

Cold air pushing Westwards across the UK on Friday

Stronger riding to the North of us and in the Atlantic moving towards Greenland, another upgrade.

[Panayiotis]

Knock Knock...Oh yes hello -10C uppers you may enter our small island! Am i going crazy lol?

Edited January 6, 2013 by Panayiotis

[Cheshire Freeze]

Not so sure about this run. That high doesn't look favoured to get to Greenland at 168 hrs

[Met4Cast]

Not so sure about this run. That high doesn't look favoured to get to Greenland at 168 hrs

It's slowly getting there

Horribly messy though, short waves all over the place, -10c 850hPa air moving into E/SE parts at this time frame though

[syed2878]

nice1 pyrotech an easy clean explaination for any new comers.

[Cheshire Freeze]

I think it will look at the upcoming low entering the image at 171hrs.

It would be nice if it could because there's a nice chunk of vortex waiting to drop down into Scandi!

[Met4Cast]

T180 here comes the toppler

Greenland High.. failed.

[swfc]

struggling at 168 hrs?flattening out and that low developing at the tip of greenland going over the top.hmmm

[Met4Cast]

struggling at 168 hrs?flattening out and that low developing at the tip of greenland going over the top.hmmm

Fortunately FI is at about T96 so I'd expect that idea to change several times over before it actually gets here. The evolution is incredibly messy, the cold trend is still there though for late next week/weekend.

[Cheshire Freeze]

T180 here comes the toppler

Greenland High.. failed.

Yep, was my concern too. Not wanting to know the ECM 12z version of events unfortunately.

[swfc]

pv goes into overdrive at 204 hrs???????

[Met4Cast]

pv goes into overdrive at 204 hrs???????

Happens with near enough every single GFS run. I don't know why the NOAA bother with the Low-Res part of the run if I'm honest

[Cheshire Freeze]

We need to see the PV split between Scani and west of Greenland to allow sufficient opportunity of ridging. Unfortunately the GFS appears to have gone cold on this idea for the moment.

[cold snap]

ukmo at 144 looks pretty good.big difference between ukmo and gfs at that timeframe